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Re: [f-cpu] Status quo



Le 2015-03-31 17:37, Cedric BAIL a ÃcritÂ:
Hello,

On Tue, Mar 31, 2015 at 5:25 PM, Nikolay Dimitrov <picmaster@xxxxxxx> wrote:
DRI uses memory managed by DRM, which does exactly what you need.
Absolutely not ! The memory allocation sure, but it never provide a
simple way to adapt to the GPU memory layout. That's why uploading
texture is usually heavy on CPU as they have to memcpy every pixel in
a different layout before uploading them to the GPU or they endup on
the GPU in a format that will be noticably slower. I have never seen a
system where you could get a linear looking memory on the CPU side via
the MMU and a tile based one in physical memory.

If I understand correctly, you need to map arbitrary rectangles in memory to a different memory layout. It's not the MMU's role, its role is to "manage" and protect memory. It is VERY hard to have pages that are not a power of two.

I seem to remember that the RPi's Broadcom chip has several DMA channels, including one with "2D" capability, it might do what you seem to describe. It takes strips of equal sizes from one memory, and puts them with different
spacings or strides somewhere else. Is that what you think of ?

yg
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